feat:theme

src/views/Preview.vue

@@ -114,7 +114,7 @@ const open = async () => {
 
 const opened = () => {
   meta2d.store.options.shadowColor = '#0000'
-  meta2d.canvas.parentElement.style.background = meta2d.store.data.background|| meta2d.store.theme[theme].background;
+  meta2d.canvas.parentElement.style.background = meta2d.store.data.background|| meta2d.store.theme[meta2d.store.data.theme].background;
   let fit: any =
     (meta2d.store.data as any).scaleMode === '3'
       ? 'height'